Update single value from script without copying table?

[Maz]

Hi,

I want to decrease the value on a specific row of a table while I'm looping another table.
I have a large list of people and I have to do calculations on each person, but for simplicity lets look at a very limited case:

I want to loop over the PersonsTable and give them their favorite fruit untill either they are satisfied or stock runs out.
Now I assume I don't want to make a new copy of the fruits table and delete the old one for every person on the person list?

Is there a simple way to say "Update row X of this Table to Y"?

FruitTable:

FruitType	Amount
Apple	10
Pear	3

Now I'm currently looping through another table based on it's row number. The table is like this:
PersonsTable:

Person_ID	FavoriteFruit	DesiredAmount
3109421	Apple	2
9271581	Pear	4
3051235	Apple	5